The Cretaceous Horsethief Batholith intrudes Helikian Purcell sediments. The intrusion is zoned from fine-grained/medium-grained granodiorite to coarse-grained quartz monzonite.

Radioactivity is associated with fractures in the quartz monzo- nite. A sample of a 1 centimetre wide quartz-muscovite vein assayed 1.7 per cent uranium, 0.01 per cent molybdenum, and 0.01 per cent tungsten. Disseminated uraninite is likely the radioactive mineral (Assessment Report 7048).

The Horsethief Batholith commonly has areas of anomalous uranium, molybdenum, and tungsten. Black sand placer concentrates in outwash gravels around the batholith contain radioactive and rare earth minerals (see 082KNE005).